Compared with a cathode ray tube (CRT) or a liquid crystal display (LCD), an organic light emitting display (OLED) has the advantages such as thinner, wider viewing angles, faster response and lower power consumption, etc. Thus, as the next generation display, the OLED has been on the focus.
An array substrate of an OLED generally includes two thin film transistors (TFTs), one of which functions as a switching transistor and the other functions as a driving transistor. FIG. 1 is a plan view showing a partial structure of an array substrate in the prior art, and FIG. 1B is a view showing a cross section of a broken line A-A in FIG. 1A. As shown in FIG. 1A and FIG. 1B, the two TFTs included in the array substrate in the prior art are a first thin film transistor TFT1 and a second thin film transistor TFT2 respectively. The specific layer structure thereof includes a transparent substrate 1, a first gate electrode 101a, a second gate electrode 101b, a gate electrode insulation layer 102, a first active layer 103a, a second active layer 103b, etch stop layer (ESL) 104, a first source electrode 105a, a first drain electrode 106a, a second source electrode 105b, a second drain electrode 106b, a resin layer 107, a metal connecting line 108, a pixel electrode 109, a black matrix 110, an organic light emitting layer 111, a counter electrode 112, a gate line 113, a data line 114 and a power line 115. The gate line 113 is connected to a gate electrode of the first thin film transistor TFT1, i.e., the first gate electrode 101a; the data line 114 is connected to a source electrode of the TFT1, i.e., the first source electrode 105a; the first drain electrode 106a of the first thin film transistor TFT1 is connected to a gate electrode of the second thin film transistor TFT2, i.e., the second gate electrode 101b through a via-hole. The power line 115 is substantially parallel with the data line 114 and connected to a source electrode of the second thin film transistor TFT2, i.e., the second source electrode 105b. A drain electrode of the second thin film transistor TFT2, i.e., the second drain electrode 106b is connected to the pixel electrode 109.
As shown in FIG. 1A and FIG. 1B, both of the first thin film transistor TFT1 and the second thin film transistor TFT2 have bottom gate structures. The first drain electrode 106a is connected to the second gate electrode 101b through a via-hole by the metal connecting line 108 which is provided on a same layer as the pixel electrode 109. The metal connecting line 108 and the pixel electrode 109 may be made of same materials and are conductive. Therefore, in order to avoid short-circuiting, a region overlaid by the pixel electrode 109 needs to be kept away from the metal connecting line 108. As shown in FIG. 1A and FIG. 1B, the organic light emitting layer 111 provided on the corresponding pixel electrode 109 needs also to be kept away from a region overlaid by the metal connecting line 108, and the region overlaid by the metal connecting line 108 is overlaid by the black matrix 110 which divides the sub-pixel regions.
In the above structure having two thin film transistors, when the drain electrode of the first thin film transistor is connected to the gate electrode of the second thin film transistor, a metal connecting line is required to be provided separately. In order to avoid forming a short circuit between the metal connecting line and other conductive metals, the metal connecting line is required be overlaid by insulating materials such as a black matrix, which causes the process to be complex.